1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus, such as a copier or a printer.
2. Related Background Art
A conventional electrophotographic image forming apparatus is, for example, a copier or a laser beam printer.
For a well known conventional image forming apparatus, such as a copier or a laser beam printer, a potential sensor is provided inside an image forming area to measure the surface potential of a photosensitive member. During warm-up, the potential of the photosensitive member is measured after the charging and after the exposure, and the primary charge current, the grid potential of the primary charger, a laser exposure light amount (or light quantity) and a developing bias are controlled and determined.
Further, in another well known image forming apparatus, when a specific time has elapsed since the power was turned on or since the warm-up was completed, the image forming apparatus prevents a change in the internal temperature by controlling the potential again, a change in the time-transient laser light amount, a change in the charge capacity due to the photosensitive member, and a potential change due to the change of the sensitivity.
However, the following problem is encountered with a conventional image forming apparatus.
Since for a high-speed apparatus the prevention of productivity reductions is important, conventionally, potential control is not provided because sufficient time can not be allocated during the performance of a continuous job, such as one that involves continuous copying or printing.
Further, when the potential measured at a short paper feeding interval is to be controlled to prevent a reduction in productivity, the uneven potential around the circumference of the photosensitive member adversely affects potential control, so that it can not appropriately be provided, and image fogging and low image density may occur.
According to the technique disclosed in Japanese Patent Application Laid-Open No. 10-228159, based on the potential corresponding to a specific location on a photosensitive member, the charging condition is changed in order to uniformly charge the photosensitive member during an image forming period. Thus, the occurrence of uneven image density during an image forming period is prevented.
However, the objective of this technique is the prevention of an occurrence of uneven image density during an image forming period, and not to prevent a time-transient change of the laser during a continuous job and a time-transient change of the potential of a photosensitive member during a continuous job.
Further, according to the technique disclosed in Japanese Patent Application Laid-Open No. 5-323741 or 5-323742, the potential at a specific location on a photosensitive member, or the average potential, is stored as a reference value, and the potential at the specific location is measured, so that a potential change on the photosensitive member can be detected.
However, with this technique, since the potential is detected at a specific location on the photosensitive member, the detection precision is unsatisfactory. Further, according to this method, position information detection means, such as a detector or a sensor, is employed for obtain the reference potential for the photosensitive member and information concerning the corresponding location of the photosensitive member, so that manufacturing costs are increased.
When, instead of the position information detection means, such as the detector or the sensor, means is employed for counting the position information for the photosensitive member using a counter and for identifying the photosensitive member area, the count information is deleted when the main body is powered off. Thus, when the main body is again powered on, the reference potential and the correlation of positions must be remeasured, so that productivity is reduced.
It is one objective of the present invention to provide an image forming apparatus that increases the image forming productivity.
It is another objective of the present invention to provide an image forming apparatus having a superior image quality that can provide appropriate control for changes of the surface potential on an image bearing member.
It is an additional objective of the present invention to provide an image forming apparatus for detecting the surface potential at a different location on an image bearing member.
It is a further objective of the present invention to provide an image forming apparatus for, when images are continuously being formed on multiple recording media, detecting the surface potential at a location on an image bearing member that corresponds to a different interval between recording media.
According to one aspect of the present invention, an image forming apparatus is provided with an image bearing member and an image formation unit for forming an image on the image bearing member. The image formation unit is includes a charger for charging the image bearing member. A potential detector detects a surface potential on the image bearing member charged by the charger. A controller controls an image formation condition of the image formation unit on the basis of a potential detected by the potential detector. The controller controls the image formation condition on the basis of a plurality of detected potentials corresponding to respectively different non-image areas between sequentially formed images.